Production of alkali metal peroxides



May 16, 1939. G. PFLEIDERER PRODUCTION OF ALKALI METAL' PEROXIDES Filed May 25, 1935 2 Sheets-Sheet 2 TIN/f INVENTOR Ge org Pflez'derer ATTORNEY Patented May 16, 1939 PATENT OFFICE PRODUCTION OF ALKALI METAL PEROXIDES Georg Pfleiderer, Lndwigshafen-on-thc-Rhine,

Germany, asslgnor to I. G. Farbenindustrie Aktiengesellschaft, Franklort-on-the-Main, Germany Application May 25. 1935, Serial No.

In Germany May 30, 1934 14 Claims.

The present invention relates to a process of producing alkali metal peroxides.

It is already known that by oxidizing with gaseous oxygen hydrazobenzene in alcoholic solution containing alkali, alkali metal peroxides are precipitated. It has also been proposed to prepare hydrogen peroxide by oxidizing a solution of "hydrazobenzene in benzene with oxygen under pressure, reducing the resulting azobenzene to hydrazobenzene again and employing the latter again for oxidation. Certain other organic compounds which contain in the molecule two hydrogen atoms which can be split off comparatively readily, such as indigo white or anthrahydroquinone, i. e., so-called leuco-compounds behave in a similar manner to hydrazobenzene.

I have found that alkali metal peroxides can a be obtained by passing an alkaline solution of compounds of the said kind, 1. e., an alkaline organic solution of an organic leuco-compound which is auto-oxidizable in alkaline solution and the auto-oxidation product of which is soluble in the solvent used, advantageously of hydrazobenzene, preferably in an alcohol, as for example ethyl alcohol, in a cycle while alternately oxidizing with oxygen or gases containing oxygen, as

for example air and reducing again, the precipitated peroxides being separated between the two operations and the substances removed from the solution (alkali and in some cases water) being replenished continuously or periodically. By using sodium, for example, as the alkali metal, peroxides the composition of which corresponds substantially to the formulae NazOaBHzO and NaHO: or,-more usually, between the two, are obtained depending on the working conditions and the water content of the alcohol employed.

The reaction of gaseous oxygen on hydrazobenzene in the presence for example of sodium alcoholate in alcoholic solution at ordinary or moderately elevated temperature and at atmospheric or increased pressure may be seen from the following equations which indicate the said two boundary cases: (a) With several per cent water content in the ,solution (b) With a very small water content in the solution In order to reproduce hydrazobenzene from the resulting azobenzene, it is preferable, among the various known methods of reduction to use alkali metal amalgam the alkali metal content of which is continuously replenished electrolytically in a second cycle. When working with 5 sodium, this proceeds according to the equation:

Just as much sodium is introduced into the solution as is used up in the oxidation according to (a) so'that there is the advantage that the necessary replenishment of sodium is effected at the same time as the reduction. In order to keep the composition of the solution constant, 15 water may also be added if necessary.

If" the oxidation, by corresponding selection of the water content, proceeds according to equation (1)) or by a reaction lying between (a) and (12'), too much sodium passes into the solution as the result of the reduction with sodium amalgam and this excess becomes greater and the alkalinity constantly increases. The excess of alkali may be precipitated by suitable precipitants, as for example in the form of sodium carbonate by means of carbon dioxide; It is more preferable, however, in the said case to effect the reduction partially by another method and only to use sodium amalgam for reduction to such an extent as corresponds to the amount of sodium precipitated with the peroxide. This maybe effected for example by dividing the oxidized solution into two parts after separation of the peroxide formed, reducing one part with sodium amalgam and the other for example with metallic zinc or directly by electrolysis or the wellknown reduction with hydrogen in the presence of catalysts, and then reuniting the two parts. Both methods of reduction may also be employed consecutively with the undivided solution.

By reason of the fact that the complete separation of the solid peroxide after the oxidation requires some time, it is preferable to allow the solution to stand between its oxidation and the separation of the precipitate.

The concentration of the single components in the solution may be varied within wide limits. The concentration of hydrazobenzene and like compounds is preferably kept somewhat below the saturation limit. For example an about 2 per cent alcoholic solution of hydrazobenzene has proved very suitable. The alkalinity may also be of different degrees but the ratio of sodium to hydrazobenzene or like compound in the reduced solution should at least correspond to the amount (a) and (b). It is preferable to employ a from 0.3 to'l.5 normal alkaline solution. like water content of the solution amounts to several per cent, preferably for example from about 4 to 8 per cent, when working according to equation (a), and at the most-about 1 per. centr-when workinglaccording' toaequationv-(b) 1 The final product, after having been washed with alcohols or other suitable organic solventsas for example carbon tetrachloride, and dried, I

is a white crystal powder which may be employed. in the same way as alkali metal peroxides pro-- pared by dry methods as an oxidizing agentlr an agent supplying oxygenorasan inii'fial'material for the preparation of :other'percompounda a such as hydrogen peroxide, perborates, peroarbonates and persulphates. I v v The nature of the invention ther described with reference to the accompany;-

ing drawings but the invention is notrestri'cted tothe particular arrangements 1 showntherein. Anarrangement suitable forcarrying out the cyclic process already describedis shown diagrammatically in Figure. 1.. ,Figure 2 shows a .cross section of intermediate container and proximately full by an outlet'v'alve V which is preferably actuated automatically The suspension passes thence into a'centrifuge Z .for the separation, of the peroxide. The solution ireed from precipitate is then passedby means of pump P to areservoir A It, then passes from the reservoir A into reduction vessel R in which it is brought into intimate contact with liquid sodium amalgam. The .separation o fthe solution from the amalgam takes placein the settling tank C; thisseparation maybe assisted by providing several suchtanks and suitable-file ters. The reduced solution which has been freed from amalgam then flows again into the-oxidation container andthe process recommences. The water vused up is replenished at a. suitable point in the cycle. The sodium amalgam flows from C into an electrolytic cell Ewherethe um content is replenished .andthen passes again into R. The stirrer in the reduction vessel B serves at the same time as the meansior promoting circulation of the amalgam because, by its centrifugal action theamalgam is raised. Naturally, a special circulating pump may also be used for circulating the amalgam, and themeans used in the process formixing,separating and circulating may bevariedin different ways.-. -.In order to avoid too greata dilution of oxygenjin the oxidation container 0 by the-gradual en-r richment of foreign gases, a small amountiof residual oxygen is preferably continuouslywith drawn from the upper part ofthe container-.0. H By reason of the fact that the precipitated peroxide has a tendency to adhere-tojthe walls of thevessels and pipes, the containers 0 and B are preferably arranged as rotary bodies and providedwith rotary scrapers which brush the walls and which either rotate slowly continuously or maybe operated byhand. The shortand wideronhecting pipes between-Q and B; and between and Ztmay-also be provided-with will now jj V 3,158,528 oi sodiumrequired according to the equations scrapers and in this" c'ase'"they'mayconsist for example of scraping rings or pistons which are displaceable in an axial direction.

Figure 2 shows an arrangement of the said kind applied to the container B and its connecting pipes. The inner wall of the container B which lies below the level ofjthe liquidis brushed :byia stripping frame a which may be rotated by a hollow axle b and which is mounted at the bot- .tom in an open guide ring-c. Special spring elements, ;which scrape the walls, may be provided .gomthe' framed. The connecting pipe witnthe container 0 is kept free by means of an open strippingring e moved backwards and forwards by means of a rod d and the connecting pipe withthe 'centrifuge"Z is kept free by the stripping ring I secured on the rod g. By the bevelled guide portion h, ..the stripper may directly force :the automatic valve V to the side. In order that the connecting pipe may not be fully open meanwhile; the ring F is wholly or partly closed by a horizontal disc. To facilitate the upward and downward movement of Lthe weight of the-rod g and,-;inparticular, the'pressure of the column of liquid'when I isin, the, connecting pipe, are

, I The mannerflin whichthe automatic: valve. V acts as a weight-loaded pinch valvextpivot point at k ;may be clearly seen fromthe drawings.

A portion of v the connection between B -and' Z is made i'rom awide comparatively flexible rubber tubewhichis preferably protected externally bya layer ofiabric. I I

What I claim is:

l. The process of producing alkali-metal peroxides which comprises passing a solution of. an alkali alcoholate and of" an ,auto-oxidizable organic leuco-compound of the-rclass consisting of hydrazobenzene and anthrahydroquinone "in a cycle while alternately oxidizingv with gaseous oxygen and reducing again partly. with alkalimetal amalgamand partly with a reducing agent containing-no alkali and noalkali-metal, the precipitated peroxides being separated between the approximately 7 counteracted. .-,by the ,,-co unter.- vweights p andP'..... r

two operations'and the-substances removed from i the solution being replenished.

2. The process of producing alkali-metal peroxides which comprises passing a solution of an alkali alcoholate andof anauto oxidizable organic leuco-compound of therclass consisting of hydrazobenzene and anthrahydroquinone "in a cycle while alternately oxidizing :with gaseous oxygen and reducing again:- partly 'withaalkali metal amalgamxand partly by the well known'reduction' with hydrogen inthe presence. of-eata .lysts, the precipitated peroxides being separated between'the-two operations and the substances removed from the. solution being replenished.

. '3. Theprocess of producing alkali metal peroxides whichi'comprises passing asolution of an the substances removedfromthe solutionbeing rreplenished. 4. The process of producing alkali metalperoxides which ,comprises a solution of analkali alcoholate and of anorganic leuco compound which is autoxidizable in alkaline solution culating solution per each mol of oxygen conand the autoxidation product of which is soluble in the solvent used, in a cycle while alternately oxidizing with gaseous oxygen and reducing again partly with alkali metal amalgam and partly with a reducing agent containing no alkali and no alkali metal, the precipitated peroxides being separated between the two operations and the substances removed from the solution being replenished.

5. The process of producing alkali metal peroxides with a regulated content of active oxygen which comprises passing a solution of an alkali alcoholate and of anorganic leuco compound which is autoxidizable in alkaline solution and the autoxidation product of which is soluble in the solvent used, in a cycle while alternately oxidizing with gaseous oxygen and reducing again partly with alkali metal amalgam and partly with a reducing agent containing no alkali and no alkali metal, separating the precipitated peroxides between the two operations and replenishing the substances removed from the solution in which, according to the desired content of active oxygen in the product, up to 8 mols of water are introduced into the circulating solution per each mol of oxygen consumed.

6. The process of producing alkali metal peroxides with a regulated content of active oxygen which comprises passing a solution of an alkali alcoholate and of an organic leuco compound which is autoxidizable in alkaline solution and the autoxidation product of which is soluble in the solvent used, in a cycle while alternately oxidizing with gaseous oxygen and reducing again partly with alkalimetal amalgam and partly by the well known reduction with hydrogen in the presence of catalysts, separating the precipitated peroxides between the two operations and replenishing the substances removed from the solution in which, according to the desired content of active oxygen in the product, up to 8 mols of water are introduced into the circulating solution per each mol of oxygen consumed.

'l. The process of producing alkali metal peroxides with a regulated content of active oxygen which comprises passing a solution of an alkali alcoholate and of an autoxidizable organic leuco compound of the class consisting of hydrazobenzene and anthrahydroquinone in a cycle while alternately oxidizing with gaseous oxygen and reducing again partly with alkali metal amalgam and partly with a reducing agent containing no alkali and no alkali metal, separating the precipitated peroxides between the two operations and replenishing the substances removed from the solution in which, according to the desired content of active oxygen in the product, up to 8 mols of water are introduced into the circulating solution per each mol of oxygen consumed.

8. The process of producing alkali metal peroxides with a regulated content of active oxygen which comprises passing a solution of an alkali alcoholate and of an autoxidizable organic leuco compound of the class consisting of hydrazobenzene and anthrahydroquinone in a cycle while alternately oxidizing with gaseous oxygen and reducing again partly with alkali metal amalgam and partly by the well known reduction with hydrogen in the presence of catalysts, separating the precipitated peroxides between the two operations and replenishing the substances removed from the solution in which, according to the desired content of active oxygen in the product, up

to 8 mols of water are introduced into the cir- 9. The process of producing alkali metal peroxides with a regulated content of active oxygen which comprises passing a solution of an alkali alcoholate and of an organic leuco compound which is autoxidizable in alkaline solution and the organic autoxidation product of which is sol-- uble in the solvent used in a cycle while alternately oxidizing with gaseous oxygen and reducing again, separating the precipitated peroxides between the two operations and replenishing the, substances removed from the solution, and con- 4 trolling the content of active oxygen in the product by maintaining a substantial amount of water in the circulating solution and adding up to 8 mols of water per each mol of oxygen.

10. The process of producing alkali metal peroxides with a regulatedcontent of active oxygen which comprises passing a solution of an alkali alcoholate and of an autoxidizable organic leuco compound of the class consisting of hydrazobenzene and anthrahydroquinone in a cycle while alternately oxidizing with gaseous oxygen and reducing again, separating the precipitated peroxides between the two operations and replenishing the substances removed from the solution, and controlling the content of active oxygen in the product bymaintaining a substantial amount of water in the circulating solution and adding up to 8 mols of water per each mol of oxygen.

11. The process of producing alkali metal peroxides with a regulated content of active oxygen which comprises passing a solution of an alkali alcoholate and of hydrazobenzene in a cycle while alternately oxidizing with gaseous oxygen and reducing again, separating the precipitated peroxides between the two operations and replenishing the substances removed from the solution, and controlling the content of active oxygen in the product by maintaining a substantial amount of water in the circulating solution and adding up to 8 mols of water per each mol of oxygen.

12. The process of producing alkali metal peroxides with a regulated content of active oxygen which comprises passing a solution of an alkali alcoholate and of an anthrahydroquinone in a cycle while alternately oxidizing with gaseous oxygen and reducing again, separating the precipitated peroxides between the two operations and replenishing the substances removed from the solution, and controlling the content of active oxygen in the product by maintaining a substantial amount of water in the circulating solution and adding up to 8 mols of water per each mol of oxygen.

13. The process of producing alkali metal peroxides with a regulated content of active oxygen which comprises passing a solution of an alkali alcoholate and of an organic leuco compound which is autoxidizable in alkaline solution and the organic autoxidation product of which is soluble in the solvent used, in a cycle while alternately oxidizing with gaseous oxygen and reducing again with alkali metal amalgam, separating the precipitated peroxides between the two operations and replenishing the substances removed from the solution, and controlling the content of active oxygen in the product by maintaining a substantial amount of water in the circulating solution and adding up to 8 mols of water per each mol of oxygen. p

14. The process of producing alkali metal peroxides with a regulated content of active oxygen which comprises passing a solution of an alkali -zene andanthrahydroquinone in a cycle while a1- 'tei-nately oxidizing with gaseous oxygen and reoperations and 'eplenishing the substances re alcoholate and of an autoxidizable organic leuco moved from the solution, and controlling the concompou'nd'of the class consisting of hydrazobentent of active oxygen in the product by maintaining a substantial amount of water in the .l circulating solution, and adding up to 8 mols of dining again with alkali metal amalgam, separatwater per each moi of oxygen.

mg the"pr'e'cipitated peroxides between the two GEORG PFLEIDERER. 

